Solar Concentrator Mirrors - How to attach? - Page 2

RobertSmalls · 03-09-11, 07:29 AM

"enough heat" for what? I don't think you've told us what the application is.

If you shine parallel rays of light on a perfectly parabolic reflector, it will focus that light to a single point. In the case of your dish, it's the point where the antenna was located. But with flat pieces of mirror, you're only approximating a parabola.

If you think about the geometry, I think you'll agree that a collector of this type with flat pieces of mirror of width x, will focus the light across an area of width x. One inch mirror fragments can concentrate light onto a 1" wide area, two foot wide mirrors will focus the light onto a 2' wide area. Is that good enough for your application?

cdig · 03-09-11, 11:18 AM

My end goal is to replace/suppliment my electric furnace and to preheat the water going into my hot water tank.

The system will be comprised of the collector, a water/antifreeze storage tank in my basement, with copper or pex coils going to a water to air heat exchanger in my furnace ducting. There will also be a loop coming into the tank to preheat the HWT cold water feed.

The collector will focus on a single point that is the same size as the mirror tiles, 1ft square, which will be a steel plate manifold with the AF pumped through it.

The idea came from the collector detailed in the "Teton Engineering's Tracking Solar Concentrator " link I posted above. From what they've done there with flat mirrors they say they can generate 1200F...

you don't seem to think this is possible with flat mirrors?

Xringer · 03-09-11, 01:36 PM

I would make the collector (Sun-to-AF) surface area a bit larger than 1'x1',
because there is always going to be some error.. Splash over energy.

These look like flat mirrors..

"National Solar Thermal Test Facility at Sandia National Laboratories,
near Albuquerque NM. Sunlight is focused on the tower,
super-heating a working fluid that can be used to run an electrical generator."

When you get near this site and look up at the focal point on the tower,
it's like looking at a really small and bright sun. Sunglasses are a must!

I've heard they can melt just about anything..

cdig · 03-09-11, 03:35 PM

That's what I'm thinking! The combined heat from 75 suns should be enough to heat my house no? What's the diff between heating a ft sq or an inch sq?

Xringer · 03-09-11, 04:33 PM

Quote:

Originally Posted by cdig

That's what I'm thinking! The combined heat from 75 suns should be enough to heat my house no? What's the diff between heating a ft sq or an inch sq?

The 1" target might melt..

Some folks around here, put new Low-E replacement windows on their homes,
and I think some of the glass might be bowed inwards,
giving some of the panes a parabolic shape..
I can see that parabolic effect in some of my Harvey windows..

Anyways, I was watching the Boston TV news and they showed how the
Low-E windows from next door neighbors was melting off Vinyl Siding!!
(And the insulation underneath the siding)!

Energy Efficient Windows Melt Vinyl Siding - Boston News Story - WCVB Boston

RobertSmalls · 03-09-11, 06:40 PM

Quote:

Originally Posted by cdig

The idea came from the collector detailed in the "Teton Engineering's Tracking Solar Concentrator " link I posted above. From what they've done there with flat mirrors they say they can generate 1200F...

you don't seem to think this is possible with flat mirrors?

Given a large enough number of flat mirrors, you could generate 1200F. But unless you're going to go with an exotic heat transfer fluid like the hundred million dollar projects do, you probably want to keep things near or even below the boiling point of water.

I do hope y'all know, temperature and heat are two distinct concepts.

cdig · 03-10-11, 02:15 PM

I wonder if anyone has a calculator out there to determine just how many mirrors = what temp? I suppose that will depend largely on the surrounding conditions tho...

Not sure what you mean by 'temp and heat being different' ? I was never much of a scholar, more of a 'do it and find out' kinda guy.

I'm not planning on generating 1200F... that would be nuts! but if I could generate enough heat to store at say 200F, I think that would be sufficient.

cdig · 03-10-11, 02:27 PM

Quote:

Originally Posted by Xringer

I would make the collector (Sun-to-AF) surface area a bit larger than 1'x1',
because there is always going to be some error.. Splash over energy.

These look like flat mirrors..

"National Solar Thermal Test Facility at Sandia National Laboratories,
near Albuquerque NM. Sunlight is focused on the tower,
super-heating a working fluid that can be used to run an electrical generator."

When you get near this site and look up at the focal point on the tower,
it's like looking at a really small and bright sun. Sunglasses are a must!

I've heard they can melt just about anything..

Hmmm... those sun towers look distinctly like grain elevators... which we have alot of around here... I wonder.

Daox · 03-10-11, 02:39 PM

You should be able to calculate the amount of energy the collectors focus fairly easily. Temperature would be a function of how quickly you dissipate or remove the energy.

RobertSmalls · 03-10-11, 06:49 PM

Quote:

Originally Posted by cdig

Not sure what you mean by 'temp and heat being different' ? I was never much of a scholar, more of a 'do it and find out' kinda guy.

. An understanding of the concept of energy is fundamental to any sort of home heating system. You should crack open Wikipedia or YouTube for some background information on the concept.

Heat is a form of energy, which is what you want to collect from the sun and move into your house. Temperature is less important. It's just a matter of how concentrated heat energy is, not a measure of how much energy you gather.

The rate at which you move energy is called power, and is measured in kW or BTU/hr.

03-09-11, 11:18 AM	#12
cdig Helper EcoRenovator Join Date: Sep 2009 Posts: 61 Thanks: 0 Thanked 1 Time in 1 Post	My end goal is to replace/suppliment my electric furnace and to preheat the water going into my hot water tank. The system will be comprised of the collector, a water/antifreeze storage tank in my basement, with copper or pex coils going to a water to air heat exchanger in my furnace ducting. There will also be a loop coming into the tank to preheat the HWT cold water feed. The collector will focus on a single point that is the same size as the mirror tiles, 1ft square, which will be a steel plate manifold with the AF pumped through it. The idea came from the collector detailed in the "Teton Engineering's Tracking Solar Concentrator " link I posted above. From what they've done there with flat mirrors they say they can generate 1200F... you don't seem to think this is possible with flat mirrors? Last edited by cdig; 03-09-11 at 11:20 AM..

03-10-11, 02:15 PM	#17
cdig Helper EcoRenovator Join Date: Sep 2009 Posts: 61 Thanks: 0 Thanked 1 Time in 1 Post	I wonder if anyone has a calculator out there to determine just how many mirrors = what temp? I suppose that will depend largely on the surrounding conditions tho... Not sure what you mean by 'temp and heat being different' ? I was never much of a scholar, more of a 'do it and find out' kinda guy. I'm not planning on generating 1200F... that would be nuts! but if I could generate enough heat to store at say 200F, I think that would be sufficient. Last edited by cdig; 03-10-11 at 02:33 PM..

03-10-11, 02:39 PM	#19
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	You should be able to calculate the amount of energy the collectors focus fairly easily. Temperature would be a function of how quickly you dissipate or remove the energy. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

03-09-11, 07:29 AM	#11
RobertSmalls Journeyman EcoRenovator Join Date: May 2009 Location: Buffalo, NY Posts: 344 Thanks: 3 Thanked 17 Times in 15 Posts	"enough heat" for what? I don't think you've told us what the application is. If you shine parallel rays of light on a perfectly parabolic reflector, it will focus that light to a single point. In the case of your dish, it's the point where the antenna was located. But with flat pieces of mirror, you're only approximating a parabola. If you think about the geometry, I think you'll agree that a collector of this type with flat pieces of mirror of width x, will focus the light across an area of width x. One inch mirror fragments can concentrate light onto a 1" wide area, two foot wide mirrors will focus the light onto a 2' wide area. Is that good enough for your application?

03-09-11, 01:36 PM	#13
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I would make the collector (Sun-to-AF) surface area a bit larger than 1'x1', because there is always going to be some error.. Splash over energy. These look like flat mirrors.. "National Solar Thermal Test Facility at Sandia National Laboratories, near Albuquerque NM. Sunlight is focused on the tower, super-heating a working fluid that can be used to run an electrical generator." When you get near this site and look up at the focal point on the tower, it's like looking at a really small and bright sun. Sunglasses are a must! I've heard they can melt just about anything..

03-09-11, 03:35 PM	#14
cdig Helper EcoRenovator Join Date: Sep 2009 Posts: 61 Thanks: 0 Thanked 1 Time in 1 Post	That's what I'm thinking! The combined heat from 75 suns should be enough to heat my house no? What's the diff between heating a ft sq or an inch sq?